Steam generator with heat exchange on the tornado-flow principle



March 12, 1968 K. R. SCHMIDT ,6

STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE Filed Aug. 5, 1966 6 Sheets-Sheet 1 March 12, 1968 K. R. SCHMIDT 3,372,678

I STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE Filed Aug. 5, 1966 6 Sheets-Sheet 2 March 12, 1968 K R. SCHMIDT 3,372,678

STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE Filed Aug. 5, 1966 6 Sheets-Sheet 5 March 12, 1968 K R. SCHMIDT STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE 6 Sheets-Sheet 4.

Filed Aug. 5, 1966 Fig.5a

March 12, 1968 K. R. SCHMIDT 3,372,678

STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE Filed Aug. 5, 1966 e Sheets-Sheet 5 March 12, 1968 K. R. SCHMIDT 3,37 7

STEAM GENERATOR WITH HEAT EXCHANGE ON THE TORNADO-FLOW PRINCIPLE Filed Aug. 5, 1966 6 Sheets-Sheet 6 Fig. 7

United States Patent Ofiice 3,372,678 Patented Mar. 12, 1968 3,372,673 STEAM GENERATOR WITH HEAT EXCHANGE N THE TORNADO-FLOW PRINCIPLE Karl Rudolf Schmidt, Erlangen, Germany, assignor to Siemens Aktiengesellschaft, Munich, Germany, a corporation of Germany Filed Aug. 5, 1966, Ser. No. 570,490 Claims priority, application Germany, Aug. 11, 1965,

s 11 Claims. or. 122-235 i nt,.....

ABSTRACT GE THE DISCLOSURE entrained fuel particles to issue a twisting rotational flow of smoke gases from the chamber into and through the interspaces along the heating surfaces, the fuel supply means being located relative to the firing chamber so as to supply fuel thereto in a direction coaxial with the tornado flow.

My invention relates to steam generators, preferably those operating on the forced flow or once-through principle, and will be described mainly with reference to generators of the vertical or tower type, although it is also applicable to steam generators of other types.

In a tower-type steam generator, the combustion chamber is upwardly continued by an elongated smoke-gas conduit space and the heat ng surfaces, consisting of systems of boiler tubes for the Water to be evaporated and the steam to be superheated, are mounted along the walls of this space. The smoke gases coming from the firing or combustion chamber pass upwardly along the tubes to heat them by radiation in the lower part of the entire system and predominantly by convection in the upper parts.

it is an object of my invention, relating to boilers of various types and preferably to tower-type boilers as just briefly described, to increase the efiiciency of the heat exchange between the smoke gases and the systems of heating surfaces.

Another object of the invention is to improve steam generators so as to ensure a higher degree of slag and ash separation and removal from the smoke gases.

Still another object of the invention is to more reliably prevent the occurrence of soot accumulations and the like on the boiler tubes of the heating surfaces.

To achieve these and various other objects mentioned hereinafter, my invention utilizes the particular properties of a circulatory fluid flow having the character of a rotational flow as it occurs in tornadoes, for which reason the phenomena involved in the present invention have been designated as tornado flow.

The following description of my invention takes into account that the technological utilization of tornado-flow phenomenon is of rather recent date and that so far a suitable terminology has not been generally adopted. For that reason, reference may be had to the detailed explanation of these phenomena and the definition of terms given in US. Patent 3,226,165 assigned to the assignee of the present invention. Reference may further be had to US. Patents, No. 3,199,268 to No. 3,199,272, all likewise assigned to the assignee of the present invention.

Briefly, the properties of the tornado-flow phenomenon of which use is made by virtue of the present invention relate to the excitation of a circulating and downwardly directed flow like the one schematically represented in FIG. 1 at PC within the firing and combustion chamber 1 of the illustrated steam generator. The circulatory flow PC is a potential flow which takes place near the generally cylindrical wall of the chamber but in spaced relation thereto so that the fluid particles that constitute the flow are not subjected to friction. The downward potential circulatory flow PC coaxially surrounds a simultaneously occurring rotational flow R which has an additional axial component in a direction opposed to the axial component of the potential circulatory flow and hence in the upward direction. The interiorly located rotational flow R is comparable to a vortex filament resembling that of a tornado in nature. In a geometrical contour plane which extends across the flow space perpendicularly to the common axis of rotation of the two flow branches PC and R just at the approximate lower end where the two branches merge with each other (as well as in one or more parallel singular planes of the potential flow PC), there are generated one or more vortex sinks or even entire sink regions. In such a sink the streamlines of the circulating potential flow PC (only one such streamline being shown for each of the flows PC, R) turn inwardly along a logarithmic spiral and become subjected to friction. At this locality the flow reverses its axial directional component to merge with the. streamlines of the upwardly driected rotational flow R. As each streamline of the potential flow PC approaches the region of the rotational flow R, the logarithmic spiral of its path becomes modified to substantially the shape of an arithmetic spiral. The sinks or sink areas in which the flow has an inwardly directed radial component, cause the occurrence of corresponding sources or source regions in which some quantity of the flow passes from the internal rotational branch R to the outer circulating flow PC and consequently has an outwardly directed radial component. Thus there occur superimposed velocity fields with strong local changes in speed or acceleration, mainly in the boundary zones between sink and source regions. These local changes in speed and acceleration impose force effects upon the particles moving with the flowing medium; and these forces-relative to an imaginary system of coordinates moving With the floW-act as relative forces or Coriolis forces.

According to the present invention, I design a steam generator in such a manner that the just-mentioned tornado-flow phenomena are excited and maintained during steam generating operation. More specifically, I design the firing or combustion chambers of the steam generator as a tornado-flow generating system from which I pass the issuing rotational flow branches or vortex filaments (corresponding to the streamline denoted by R in FIG. 1) through the smoke-gas conduit system of the steam generator in which the systems of heating surfaces are located, so that the heating surfaces are subjected to heat exchange with the rotational flow or with tornado flows excited thereby. Consequently, I utilize a phenomenon akin to the natural funnel or spout of a tornado for the purpose of efficiently passing the heat, generated in the firing or combustion chamber, to the heating surfaces of the steam generator.

According to another feature of my invention, I generate the tornado flow by exciting a circulatory fiow motion within the combustion chamber. For this purpose I provide the wall of a substantially rotationally symmetrical, preferably cylindrical combustion chamber with a number of injection tubes or nozzles for supplying a portion of the combustion or fresh air or recycled quantities of smoke gas which excite the primary potential flow (PC in FIG. 1) along the inner wall surface of the chamber. For this purpose the injection tubes or nozzles enter into the chamber in a tangential and downwardly inclined direction.

According to another feature of my invention I supply the remainder of the fresh air, charged with pulverulent solid or with liquid fuel, through a coaxial inlet opening at the bottom of the firing chamber, similar to the fuel inlet location in a cyclone-type firing chamber. However, the fuel may also be injected through several openings or nozzles extending in the axial direction so as to directly enter into the rotational flow (R in FIG. 1). In the latter case, it is desirable to impart a pre-excitation to the rotational fiow (R) such as obtained by a simultaneous provision and use of the above-mentioned tangentially and inclined lateral injection nozzles. At the entering localities of the centrally located fuel-laden fiow, its axial components are opposed to those of the potential circulating flow (PC), so that one or more quiescent planescorresponding to a rough ground-will occur above which the above-described vortex sink regions are generated.

The invention will be further described with reference to the accompanying drawings showing by way of example several embodiments of steam generators according to the invention.

FIG. 1 is a schematic and sectional illustration of a tower-type steam generator in conjunction with the diagram of an electric power generating plant of which the steam generator forms part.

FIGS. 2 and 3 illustrate schematically and in section two different embodiments of part of a steam generator according to the invention otherwise similar to that of FIG. 1

FIG. 4 is a schematic cross-sectional view taken through another steam generator.

FIGS. 5a and 5b illustrate partly a side elevation and a longitudinal section through part of the steam generator according to FIG. 1.

FIGS. 6a, 6b and 6c show respectively a lateral View, a partial cross section and a sectional detail of a different embodiment of heating surfaces applicable in a steam generator according to the invention; and

FIG. 7 is a schematic illustration of another embodiment of a steam generator according to the invention.

The same reference characters are applied in the various illustrations for functionally corresponding components respectively.

Referring to FIG. 1, there is shown a tornado-flow boiler of the tower-type. Located above the firing and combustion chamber 1 is gas conduit path 2 with a system of heating surfaces 15. The conduit space has an essentially hollow cylindrical configuration, the heating surfaces 15, such as evaporator sections and superheater sections, being distributed over the inner surface area of the hol- 10w cylinder. The top of the tower structure comprises a tornado-flow dust separator 3. The generated steam is supplied to a set of turbines T driving an electric generator G. Feed water for the steam generator is supplied from a condenser C through a pump P which delivers it through regenerative preheaters PH, heated by steam from the turbines, to a tank WT and through further preheaters PH. (Plant details at the end of this specification.)

Fuel is supplied at F and combustion air at A. The air is preheated at AH and supplied to nozzles 7, 12 still to be described. Part of the air is also used for propulsion and injection of the fuel.

As will be more fully explained below, a tornado flow is excited in the interior of the firing chamber 1 and is maintained in such a manner as to produce a potential circulating flow PC in the outer region near the wall of the top portion in the firing chamber, this potential flow circulating downwardly until it reaches the lower region of the firing chamber where the flow reverses its direction and is converted into a uniformly rotating rotational fiow R, corresponding to a vortex filament that extends upwardly in the central region of the firing chamber until it leaves this chamber through the opening of a diaphragm 9 to pass through the smoke-gas conduit constituted or lined by the system of heating surfaces 15.

Particulate, namely liquid or pulverulent fuel is supplied in the direction of the arrow 4 through a lower coaxial inlet tube 5 which protrudes upwardly into the firing chamber 1 up to a sufficient height to form an annular chamber at the bottom of the firing chamber. The outlet opening of the inlet tube 5 is provided with guiding elements, for example vanes or louvers 6 which impart a pre-twist to the entering medium. In this manner, the supply of the fuel is used for pre exciting the rotational flow R which in some cases sufiices to produce the abovedescribed tornado flow but preferably is employed in addition to other means of excitation still to be described.

The fuel particles, supplied in pulverulent form or as droplets, may be given an admixture of some of the cumbustion air, for example 30% thereof, or an addition of recycled smoke gases which may be supplied after they have been used for drying or preheating purposes. The added air or smoke gas then serves to effect or control the transportation of the fuel. Another portion of the fresh air, for example 20%, or also recycled smoke gas, is injected into the top portion of the firing chamber through a number of lateral nozzles 7 and 8. If desired, further fuel may be admixed to the gas supplied to these nozzles. The nozzles 7 and 8 have their respective axes directed in opposition to the advancing direction of the central rotational flow R. That is, the nozzles extend tangentially with respect to the wall of the firing chamber (FIG. 4) and also in a downwardly inclined direction. In this manner, the injected flow medium excites the potential circulating flow PC which moves downwardly in the immediate vicinity of the firing chamber wall.

A diaphragm-shaped wall portion 9 at the top of the firing chamber, having a conical shape in the illustrated embodiment, reduces the cross section of the gases passing from the firing chamber 1 into the conduit portion 2 of the steam generator, thus causing an increase of pressure in the potential flow and thereby preventing the formation of a secondary-air jet. The space 33 immediately above the diaphragm 9 forms a distribution chamber.

From the potential circulating flow PC in the upper portion of the firing chamber, there extends a branch down into the ring-shaped space 10 around the fuel inlet duct 5. This space communicates with drains 11 for removal of ash and slag. The residual portion of the fresh air, for example 50%, or also recycled smoke gas, may be supplied to the annular space 10, and this may also be done by secondary-gas nozzles similar to those denoted by 7 or 8, or by other suitable inlets such as those schematically represented by nozzles 12. The dimensions and angular positions of the nozzles 12, as well as the pressure and flow speed of the gas injected through these nozzles, are so chosen that particle rings are formed between each two nozzles or nozzle groups mounted above each other, each ring being formed by the outer particles or droplets of the fuel to be burned or already burned. The rings are kept floating for a time sufficient for the combustion of the fuel particles, before each ring discharges to the next lower ring and ultimately is dissolved in order to pass the remaining ash through the drains 11.

The fuel particles issuing from the twist nozzle 6 of the inlet 5 enter into the influence of the superimposed velocity fields in the boundary or mixing region between rotational fiow R and potential circulating flow PC. As a result, the particles are driven from the entering point in the outward direction where they collect in the region of the potential circulating flow PC and become transported into the ring space 10 surrounding the inlet beneath the twisting nozzle 6. After passing through the twisting nozzle 6, the fuel particles leaving the inlet travel at high speed initially on helical or spiral paths into the fuel particle strand which thus builds up the first floating fuel ring. During this travel, the fuel particles are initially exposed to the high temperatures of the firing chamber so that degassing of the particles commences, although the combustion proper will take place subsequently in the fuel-particle rings rotating while being suspended at the height of the twisting nozzle 6 and beneath this nozzle.

Each of these rotating ring-shaped accumulations of fuel particles has a given storage capacity for particles. Consequently, each rotating ring can accumulate only a given weight or a given mass of particles. If this capacity is exceeded, the ring, when properly excited, will issue the excess to the next lower ring. For example, a coal particle which, by virtue of the separating effect near and in the tornado flow phenomenon, was entrained from the fuel inlet into the uppermost ring, will after some time migrate into the next lower ring, thereafter into the sec- 0nd lower ring, and so stepwise from ring to ring until it gradually is fully combusted. The remaining particles of ash and slag pass from the lowermost dust ring ultimately into the drains 11.

The phenomena just described are not predicated upon providing a firing chamber of the upright or vertical type exemplified in FIG. 1. The rotating rings are kept stable by the injected secondary gas to such an extent that the rings will form in the same manner regardless of their position in space and will in the same manner discharge some of their contents to the next following ring-shaped accumulation if overloaded. As mentioned above, it is in some cases preferable to supply a portion of the fuel or even the entire amount of fuel through the nozzles for injecting the secondary air or gas. This expedient is also applicable when different fuels are simultaneously employed and is suitable with coal dust or other solid fuels as well as with liquid fuel. The above-mentioned phenomena occurring in the steam generator and the resulting' operations and advantages will be more fully explained presently.

The firing or combustion chamber operates as a vortex chamber in which the forces produced by the coaction of potential flow and rotational flow have the effect of guiding the fuel particles during combustion on defined paths situated substantially on curved rotationally symmetrical geometric surfaces while the combustion takes place. A prerequisite for proper operation is the difference in gravity between fuel particles and gas particles. Thespecifically heavier fuel particles collect in the mixing zone between potential circulatory flow and rotational flow. This can be utilized for example with coal-dust firing, to keep the coal particles on given paths so that with a sufiicient supply of oxygen an intensive combustion will take place. Furthermore, a potential-flow branch splitting from the main flow where the potential circulating flow enters into the main vortex sink, is utilized for discharging the dust particles from the mixing zone. The dwell time and the travel distance of the burning coal-dust particles may be dimensioned by the particular kind of flow excitation, so that the combustion is terminated at the locality where the particles are thus eliminated. Consequently, the re sidual ash or slag can be readily drained from the firing chamber. The tornado'flow phenomena within the firing chamber thus have the double effect of securing an intensive combustion, on the one hand, and securing immediately thereafter the removal of ash and slag particles, on the other hand. Accordingly, the smoke gases leave the firing and combustion portion 1 of the steam generator in a. largely cleaned condition as they pass between the heating surfaces 15.

Depending upon the kind and composition of the fuel, it is sometimes advisableto add a portion or even the entire fuel to the excitation gas (fresh air and/ or recycled smoke gas) which is injected through the inclined tangential nozzles 7, 8 for exciting the potential circulatory flow. The injection nozzles for the fuel in the latter case are either combined so as to carry fuel as well as the excitation gas, or they are mounted as separate fuel injection nozzles.

Both types of gas and fuel supply may be continuous, or the supply may be made pulsating, for example by passing the fluid quantity over a sharp edge or other means known for this purpose. In any event, the excitation of the tornado flow in accordance with the invention requires a substantially accurate tangential injection of the fluid media relative to the cylindrical walls of the firing or combination chamber itself, and not relative to another, imaginary circle or cylinder concentric to the combustion chamber as is the case with some conventional cyclone-type firing systems. Of considerable significance, in conjunction with an inclined tangential supply of all gases and of the fuel, is the shape of the chamber bottom. This bottom must be given such a shape that the sink flow, which develops above this bottom, is not interfered With at any locality. That is, the formation of the vortex sink in a rotationally symmetrical shape and in coaxial relation to the axis of rotation must remain possible. It is therefore particularly favorable to give the chamber bottom a convex shape at least in the middle so that it bulges in the direction of the axial component of the rotational flow. This is shown at 34 in FIGS. 2 and 3. In this manner, the mixed flow becomes forced apart and occupies an axially wider region than otherwise.

The diaphragm 9 increases the pressure in the potential flow PC. This diaphragm need not possess the shape of a collar or of a tube which protrudes downwardly into the combustion chamber as is the case with cyclone firing systems. The contour of the diaphragm, which must be very accurately coaxial to the rotational axis of the flow, is given such a shape that the resulting increase in pressure is as effective as feasible. Preferred shapes of diaphragm i as shown in FIGS. 2, 3 are still to be described. Particularly the potential flow PC should not be forced outwardly by a conical shape of the diaphragm or by a corresponding conical shape of the smoke-gas conduit system 2. The smoke gases issue from the combustion chamber through the opening of the diaphragm $9 and possess at this locality an intensive rotational component or twist which is maintained along the next following longitudinal extent of the smoke-gas conduit system in which the smoke gases are in heat-exchanging relation to the heating surfaces.

It is desirable to provide for predetermined dwell times of the fuel particles in the firing and combustion chamher and consequently for accurately determined combustion or consumption periods for the fuel particles. For this purpose, care is taken to enforce in. the lower portion of the chamber 1 a circular path of the. fuel particles and to cause the-m to accumulate in the above-mentioned particle rings which rotate about the main axis, and to cause the particles to jump from time to time from one particle ring to the next lower ring. This, according to the invention is also achieved by the tornado-flow phenomenon but with a type of excitation particularly suited for such a formation of dust rings. One way of doing this is to provide the bottom portion of the firing chamber with the tangential injection ducts or nozzles 12 (FIG. 1) which are located in a horizontal plane rather than being downwardly inclined. The nozzles 12 may be arranged vertically above one another or, for example, on helical lines in staggered relation to each other. Each nozzle jet entering in a horizontally tangential direction will spread in opposite axial directions, namely inclined upwardly and inclined downwardly. At those localities where the downwardly directed jet portion of a nozzle meets with the upwardly directed jet from a lower nozzle, the axial velocity component in the potential flow PC becomes equal to zero. Thus there occurs within the flow field a ring-shaped, rotating quiescent or mixing zone in which the fuel particles accumulate and form a ring in which the particles rotate and simultaneously can burn out. (The similarity of the just-mentioned ring formation to a smoke ring blown by a cigarette smoker will be recognized.)

In order to have several such rings floating and rotating one axially above the other, the axial component of the potential flow must alternatively be directed downwardlythen assume the zero valuethen be directed upwardly thereafter be directed downwardly then becomes equal to zero, and so forth. This change in direction of the axial component with successive zero passages is obtained by providing several nozzle groups 12, each group occupying the same height or level, above one another, the nozzles of each group blowing tangentially to the chamber wall into the chamber space.

According to another feature of the invention, the lower portion of the combustion chamber 1 is designed in the manner just described, whereas the upper portion of the same chamber is designed in accordance with a tornado-flow dust separator. This has the result that the fuel particles supplied into the combustion chamber are entrained by the potential fiow into the uppermost one of the floatingly rotating fuel-particle rings.

, As mentioned, each of such rings has a limited particleretaining capacity depending upon the flow conditions and upon the particle mass. When this capacity is exceeded, or if the axial components of the flow are changed, a portion of the fuel particles, under the conjoint etfect of gravity, drops into the next lower ring, and so forth. That is, when a ring becomes overloaded, it will first discharge into the next lower ring and then commences to be newly built up by renewed enrichment with freshly supplied fuel particles. Since virtually any desired number of such rings can be produced in which the particles do not touch the walls of the cylindrical flow chamber, any desired dwell periods, reaction periods, combustion periods and other combustion conditions can be secured, before the particles are drawn from the lowermost ring into the dust-discharge outlet or drain while being in molten-liquid or dry condition.

While the ring formation has been described with reference to a vertical axis, the same principle and excitation means also apply to a firing chamber having a horizontal axis.

The embodiments illustrated in FIGS. 2 and 3 constitute modifications of the steam generator illustrated in FIG. 1. According to FIG. 2, the nozzles 7 and 8 are arranged in nozzle groups which are oriented in an inclined tangential direction opposed to the flow direction of the fuel entering through the inlet conduit 5, this fuel flow direction being represented by the arrow 4. The inclination of the injection nozzles at some localities may be at a shallower angle in one nozzle group than in the other. Similarly, the injection nozzles 12 are arranged in groups. In contrast to the embodiment of FIG. 1, the injection nozzles 12 shown in FIG. 2 are given an inclined direction so that the nozzle axes point downwardly. Furthermore, the bottom 34 of the firing chamber is given a different shape in order to place the drain for slag and ash at the outer periphery. The diaphragm 9 has the shape of a concave ring, seen from the direction of the firing chamber. This results in a hook-shaped cross section of the diaphragm 9 by virtue of which the distribution space 33 above the diaphragm becomes enlarged in comparison with that shown in FIG. 1.

In the embodiment of FIG. 3, fuel is supplied through the lateral injection nozzles 7a, 8a and 7b, 8b. With this type of fuel supply, the fuel inlet tube may be reduced in diameter or may be omitted, if desired. Furthermore, the inlet conduit 5 may also be used for exclusively supplying recycled smoke gas or fresh air to assist in the excitation of the tornado flow by virtue of the twist imparted to the inflowing gas by the nozzle 6.

In the embodiment of FIG. 3, the lower lateral nozzles, may extend radially, as shown at 12a, that is, they need not be inclined downwardly. Furthermore, the lateral nozzles may have ultimately opposed axially inclined directions as shown at 1222. Due to such inclined positions, and as described above, the rotating fuel particle rings can be kept floating in defined positions. The ash drain 11 is preferably located in the radially outer portion of the firing chamber bottom 34.

A horizontal arrangement of the firing chamber or burners permits connecting several firing chambers to a common vertically upright combustion chamber, for example in the manner illustrated in FIG. 4. Three firing chambers 31, 31 and 31 are connected tangentially to a rotationally symmetrical combustion chamber 13. A circulating flow can be excited in the combustion chamber 13 and can be maintained in the manner explained above with reference to FIG. 1. The circulating flow, in turn, excites a twisting flow, namely a rotational upward flow of the vortex filament type, passing through the heating surfaces which surround the latter flow substantially in the shape of a hollow cylinder. The outlets 14, 14 and A of the respective firing chambers correspond to the nozzles 7 and 8 in FIG. 1. Consequently, they excite the rotational fiow by exciting a primary potential circulating flow. Such a type of design also affords mounting firing chambers in respectively different planes or levels, so that any desired large number of such firing chambers or burners can be connected to the same combustion chamber. In addition to the tangential or preferably inclined tangential arrangement of the firing chambers, the outlets of other firing chambers may communicate with the central portion of the combustion chamber 13 in order to excite the rotational flow in the combustion chamber. These inlets may be provided with devices for producing a twist corresponding to the twisting nozzle 6 at the end of the inlet conduit 5 in FIG. 1. The latter expedient is used exclusively for exciting the tornado flow phenomena or it may serve only to assist in the excitation.

With any of the embodiments exemplified by FIGS. 1, 2, 3 or 4, the provision of a sufiicient number of peripherally distributed injection nozzles for secondary air in one or several levels above or also below the opening of the fuel inlet 5, afford adjusting the dwell time of the fuel particles accumulated in the floating rings and consequently adjusting the degree of combustion. Since the portion of the firing chamber above the fuel inlet opening is designed in a manner of tornado-flow dust separator, virtually all fuel particles are subjected to a separation process. As a result, a complete removal of slag or dust by virtue of the separating effect within the firing and combustion spaces themselves can be secured. The dust separation takes place not only during the complete burning of the particles but already prior thereto. The adjustable dwell time and the adjustable degree of combustion of the fuel particles prevents the occurrence of after-burning effects behind the combustion chamber. It further prevents the occurrence of local temperature peaks thus obviating the danger of evaporating silicic acid. In addition, the described design of the combustion chamber affords the possibility of a more accurate computation of the fiow phenomena than the conventional combustion chambers.

Reverting to FIG. 1, 2 or 3, it will be seen that the heating surfaces 15 upwardly adjacent to the combustion chamber 1 comprises a system of boiler tubes arranged on a cylinder and coaxially within each other. The rotational flow of smoke gases issuing from the combustion chamber 1 produces a twisting flow within the individual annular interspaces between the heating surfaces of the boiler tubes. Preferably, additional flow excitation means are provided for augmenting the twisting flow through these annular interspacesv The twisting flow effectively increases the heat exchange. This can be explained by taking into account that the twisting flow extends over a much longer "travel path than a purely axial flow and that the speed of the flow along the contacting surfaces of the boiler tubes is much greater. If, further, the tubular systents of the boiler are arranged in accordance with the known concentric arrangement mentioned above, the heating surfaces are subjected to heat exchange on both sides thereof.

In the embodiment schematically shown in FIG. 1, a total of eight tubular systems 15, extending on concentric circles or cylinders are suspended so that a free expansion in the vertically downward direction is possible. The suspension of the individual systems of tubes may be such that the individual cylindrical heating surfaces may also expand differently from each other. This is achieved simply by separately suspending the individual heating surfaces located on the same cylinder.

FIG. a shows a plan view and FIG. 5b longitudinal section of a boiler portion in which the heating surfaces are connected to the boiler circulating system. The quantity of working medium to be heated, evaporated and superheated in the steam generator passes through cylindrical tubular heating surfaces in the form of cylindrical heating surfaces coaxially stuck into each other. The tubes of a cylindrical heating surface terminate alternately in two or more ring-shaped collectors 16, 17 arranged one above the other. The inner ring-shaped collectors 16 and 17 are connected by tubes 20, 21 with outer ringshaped collector l8 and '19. By means of such a group of collectors the working medium (water or steam) may be supplied into the boiler as well as conducted out of the boiler. It will be understood that the above-mentioned cylindrical systems of tubular heating surfaces comprise in the conventional manner the evaporator portion and the super-heater portion as well as any intermediate superheaters or reheaters.

The twisting motion of the smoke gases excited between the heating surfaces from the flow within the combustion chamber decays gradually and would become negligible after the smoke gases have passed through some length of travel. As mentioned, however, means are provided for maintaining the twisting flow. For example, the heating surfaces themselves are given the formation of a twisting guide or separate twisting guides (FIGS. 6a to 6c) may be provided. Another way is to provide guide vanes of sheet metal in the annular interspaces between the concentric heating surfaces. Still another way of reexcitating the twist is to give the smoke-gas conduit path a sharply curved course, for example the design of a rectangular knee (FIG. 7). This permits obtaining a tangential entrance of the flow between the annular interstices of the vertical portion and of the horizontal portion of the conduit system, such tangential entering having the effect of exciting a twisting motion.

In the embodiment shown in FIGS. 6a, 6b and 6c, cylindrical heating surfaces are provided at their respective ends with ring-shaped collectors of the type just described and thus form an integral structural unit having the length It. Such a unit can be prefabricated, at least to a major extent, and then be assembled with other units at the site of the steam generating or power plant. The heating surfaces can then be serially joined with each other outside of the boiler proper. Consequently the connection can be readily corrected subsequently if needed. The cylindrical heating surface 22 has its lower end extend down to the boiler portion 23 which forms the terminal structure where the interior ring-shaped collectors of the individual cylindrical heating surfaces, as well as the connecting tubes leading to the external ring-shaped collectors, are located. This terminal structure 23 is further provided with tubular passages 24 for the smoke gas which are so oriented that the smoke gas passing through the openings 24 between the series connected cylindrical heating surfaces is given a new twist when leaving each seciii tion or unit. In this manner, the highest speed of the smoke gas flow is each time excited in the middle of the gap between the terminal structures of the mutually adjacent boiler units.

The renewed excitation of the twist upon passage of the smoke gas through a relatively long travel path may also be effected with the aid of an angle or knee in the flow conduit system, for example by changing the flow direction by about This manner of re-excitation is embodied in the tornado-flow boiler shown in FIG. 7. The system of heating surfaces is divided into two portions 2 and 25 sequentially traversed by the smoke gases. That is, the first vertical system 2 is followed by another system or portion 25 of heating surfaces whose axis is horizontal. The ring-shaped gaps of the vertical heatingsurface system 2 are eccentrically displaced relative to those of the horizontal system 25 in order to thereby obtain an approximately tangential entrance of the flow into the annular gaps of the horizontal system 25. The knee 26 may be combined with a supply or discharge of liquid or vaporous working medium (water or steam).

The dust particles not separated within the combustion chamber as well as any dust particles as may subsequently evolve, for example due to sublimation, collect in the annular interspaces between the cylindrical heating surfaces in the form of strands or flow filaments. Consequently, they do not touch the heating surfaces so that these will not be so coated with slag or soil. This minimizes or virtually eliminates the need for blowing a boiler in order to remove soot or for applying other expedients for cleaning the heating surfaces.

In the vicinity of the axis within the smoke gas conduits there obtains a flow whose character is that of a rotational flow. Such a flow along an axis can be substituted, at least partially, by a solid cylindrical or streamlined body without thereby substantially changing the essential properties of the tornado flow phenomena. Applying this concept to the coaxial arrangement of cylindrical heating surface systems in the tornadodlow boiler, it will be recognized that the inner heating surface within any of the annular interstices between two systems may be looked upon as constituting such a solid cylindrical body.

Any residual slight amounts of fly ash not separated Within the combustion chamber, travel with the combustion gases between the heating surfaces toward the outlet of the smoke-gas conduit where preferably a dust separator 3 (FIG. 1) is located.

The dust separator is preferably also based upon the tornado-flow principle, such dust separators being known as such from the above-mentioned Patents No. 3,199,268 and No. 3,199,271. If at this point the twisting flow of the smoke gases has already decayed considerably, it is again preferable to provide for re-excitation of the twisting flow. For example, rotation-exciting guidance members and/or inclined tangential inlet tubes or nozzles may be provided in order to produce dust filaments in the mixing zone between potential circulatory flow and rotational flow, which filaments are passed to dust outlet openings.

Since in a steam generator according to the invention, the radiation portion of the tube system is not called upon to perform firing or com'bustion-technological purposes, such a portion need not necessarily be employed in the conventional manner. That is, the system of tubular heating surfaces immediately behind the outlet diaphragm 9 (FIGS. 1-3) or distributor chamber 33 need not be limited to the inner wall of the radiation space but may also occupy the entire inner space. It is of advantage, as described, to arrange a large number of parallel tubes on concentric circles to serve as heating surfaces. By virtue of the improved heat transfer achieved by the twisting flow of the gases, high heat quantities can be supplied to the boiler tubes and hence to the Working medium at numerous localities in the interior of the gasconducting cross section. As a result, relatively high thermal loadings are obtainable so that highly effective 1 1 heating surfaces can be concentrated upon a relatively small space. Heating surfaces which otherwise require three or more conduit passages can now be accommodated within a single passage. For example, evaporator heating surfaces may be formed of tubes which ascend at continuous inclination in the form of helical windings of parallel tubes. Applicable, however, are tubes or tubesystems which extend straight through the smokegas conduit space and which, with a vertical type of boiler, are suspended from above so that they can freely expand downwardly and independently of each other under the effect of heat. A horizontal type of tube systems, however, is likewise applicable. The flow of the smoke gases coming from the combustion chamber then passes through the annular interspaces between the hollow cylindrical and coaxially arranged heating surfaces. Within these annular interspaces, the hot smoke gases, issuing from the combustion chamber in the form of a rotational flow (R in FIG. 1) travel along helical streamlines. The rotational flow coming from the combustion chamber then excites in the annular interspaces a twisting movement of the smoke-gas current which is at least similar to a rotational fiow. All of the heating surfaces, with the exception of the one extending along the outermost periphery, are thus heated from the inside as well as from the outside by heat exchange with the twisting flow of hot smoke gases. The boundary conditions at the sides of the heating surfaces that border the respective interspaces at the outer side, have the effect that these heating-surface sides cannot be impinged upon by dust or slag particles so that no deposition and no frictional wear at these heating surfaces will result. Since in the smoke-gas conduit the twisting flow of the smoke gases, originally excited in the combustion chamber, is being maintained or re-excited, a significant property of this type of flow can be utilized to advantage, namely the fact that the particles of the higher specific weight, namely the dust and slag particles, form a strand or vortex filament which moves forward without directly touch ing the walls. Consequently, there is no danger of deposition and incrusta'tion on the tubes or the conduit walls, nor is there an appreciable danger of erosion as observed in other types of systems where the sometimes sharpedged ash particles can scrape along the tubes and walls.

Particularly with an axial supply of the fuel, a very uniform temperature distribution in the combustion chamber can be obtained by suitable supply of fresh air and/ or recycled smoke gases, since with this type of fuel supply no extreme local temperatures can occur at the outlet openings of individual burners or nozzles. As a result, the median temperature becomes approximately equal to the maximum temperature which on account of the good controllability of all operations can be kept on or below any desired predetermined value. For example, the temperature can thus be controlled to remain below the vaporization temperature of SiO which is about 1600 C. This contributes to providing favorable conditions toward avoiding clogging or incrustation of the smoke-gas conduit or heating surfaces by deposition of slag.

In addition, any fragments of fuel particles which may burst when burning, for example coal particles, are driven back into the floating rings enriched with fuel particles. This effect is due to the above-described superposition of the velocity fields occurring with the tornado-flow phenomena described. Consequently, any such fragments are not further entrained by the smoke gases and do not reach the smoke-gas conduits or flue passages to which the combustion chamber is connected.

The above-described effects, namely the virtually complete combustion of the fuel particles, the prevention of entrainment of particle fragments and the possibility of maintaining predetermined and relatively close temperature tolerances, for example in view of SiO vaporization, conjointly improve the operating conditions of the entire steam generating plant because a radiation portion,

conventionally provided immediately adjacent to the combustion chamber, can be fully or partially avoided, since all of the purposes to be served by the radiation portion are already satisfied by the above-described effects occurring in the firing and combustion chamber.

This has the further consequence that according to the invention the advantages of the turbulent flame enclosed within the firing chamber proper can be taken advantage of. According to Longwell, the combustion rate in an open flame increases when passing from a laminar to a turbulent fiow by the factor three, but with an enclosed flame by a factor fifty. In the latter case, combustion energies in the order of million kcal./m. h. have been measured. These phenomena have so far been observed only with gaseous or liquid fuels. However, an analogous tendency is observable also with comminuted solid fuels. It has been found, for example, that the advantages of a pulsating firing process, such as in the so-called Schmidt tube, are applicable for any kind of fuel.

On the other hand, with a firing and combustion chamber according to the invention as described above, there is the possibility of incurring excessive thermal loading so that on the Water-steam side of the boiler system, that is, within a portion of the tubes that form the walls of the combustion chamber, the phenomenon of film vaporization may occur. To avoid this effect or rendering it harmless, several expedients are applicable. For example, turbulence generating means may be provided at the inside of the tubes, sufficiently high flow velocities of the working medium and sufficiently high pressures (in the vicinity or above the critical pressure) may be applied, or a twisting flow within the boiler tubes may be employed.

As far as boiler regulation is concerned, it is preferable to adjust the secondary-gas quantities and pressures injected through the tangential nozzles to such values that all fluctuations are overcontrolled. When operating under partial load, the secondary-gas quantities are correspondingly regulated to lower values. Such systems can be operated at negative pressure as well as superatmospheric pressure.

A combustion occurring in the above-described manner within a conibuston chamber according to the invention may be looked upon as constituting a chemical reaction between solid or liquid particles and one or several gases. The above-described principles therefore, are also applicable to other chemical reactions of the same general type, in order to accelerate chemical or physical processes, such as the absorption of gases in particles or for drying purposes and the like. Any heat of reaction then liberated can be reduced in an auxiliary boiler or steam generator. The latter boiler may constitute a portion of a steam generator according to the invention whose smoke-gas conduit and heating-surface system are designed for developing a tornado flow as set forth in this specification.

Reverting now to FIG. 1, a more detailed description of the illustrated power plant will be given, although it will be understood that the following details do not form part of the invention proper and may be modified in various respects.

The superheated steam issuing from the steam generator passes through a main line into the high-pressure portion 101 of the multi-stage turbine T and thence through a line 102 and an intermediate superheater 103 into the medium-pressure portion 104 of the turbine from which the steam passes through a line 105 to the low-pressure portion 106. The turbine portions have a common shaft which drives the generator 107 (G). From the low-pressure stage 106 the steam passes through the line 108 through the condenser 109 and is then forced by the pump 110 through the low-pressure heat exchangers (preheaters PH) 111, 112, 113 and 114 into the feed water tank 115 from which it is forced by the feed water pump 116 through high-pressure heat exchangers (preheaters PH) 117, 118, 119, 12% and through line 121 back to the steam generator. The preheaters 111 to 114 are supplied with steam from corresponding taps of the low-pressure turbine 196. The high-pressure preheaters 117 to 119 receive steam from corresponding taps of the turbine stage 104.

It will be understood that the how diagram described is presented only by Way of example. Any other purpose, layout, and subdivision of the steam-consuming equipment may also be served by a tornado-flow steam generator according to the invention.

I claim:

1. With a steam generator comprising a substantially rotationally symmetrical firing chamber with fuel supply means and combustion air supply means, a smoke-gas conduit structure forming a substantially rotationally symmetrical conduit path communicating with said chamber to receive hot combustion gases therefrom, and heating surfaces extending inside and along said conduit and forming longitudinal interspaces for the passage of the gases, in combination the improvement comprising tornado-flow excitation means joined with said chamber and including at least one of said supply means for producing and maintaining in said firing chamber a tornado-flow of gasentrained fuel particles to issue a twisting rotational flow of smoke gases from said chamber into and through said interspaces along said heating surfaces, the fuel supply means being located relative to the firing chamber for supplying fuel thereto in an upward direction coaxial with said tornado-flow 2. A steam generator according to claim 1, comprising re-excitation means in the conduit path within said structure, said re-excitation means being spaced from said firing chamber for re-exciting said rotational flow of the smoke gases along their travel through said conduit structure.

3. With a steam generator comprising a substantially rotationally symmetrical firing chamber with fuel supply means and combustion air supply means, a smoke-gas conduit structure forming a substantially rotationally symmetrical conduit path communicating With said chamber to receive hot combustion gases therefrom, and heating surfaces extending inside and along said conduit and forming longitudinal interspaces for the passage of the gases, in combination the improvement comprising tornado-flow excitation means joined with said chamber and including at least one of said supply means for producing and maintaining in said firing chamber a tornado-flow of gas-entrained fuel particles to issue a twisting rotational flow of smoke gases from said chamber into and through said interspaces along said heating surfaces, re-excitation means in the conduit path within said structure, said reexcitation means being spaced from said firing chamber for re-exciting said rotational flow of the smoke gases along their travel through said conduit structure, and a plurality of sequential heating surface units of which each comprises a group of generally cylindrical arrays of heating surfaces arranged coaxially in radially spaced relation so that said interspaces are substantially formed by the annular spaces between each two of said coaxial arrays, and said re-excitation means being located between said respective units to impart new twisting motion to the smoke gases as they pass from one to the next unit.

4. In a steam generator according to claim 3, said reexcitation means comprising gas passages extending in an inclined direction realtive to the flow axis.

5. In a steam generator according to claim 3, said heating-surface units having respective axes extending at an angle to each other, and said re-excitation means forming a knee'type structure joining the interspaces of one of said units with those of the other so as to cause the smoke gases to enter from said one into said other unit at an angle to thereby increase the twisting motion of the gases.

6. With a steam generator comprising a substantially rotationally symmetrical firing chamber with fuel supply means and combustion air supply means, a smoke-gas conduit structure forming a substantially rotationally symmetrical conduit path comunicating with said chamber to receive hot combustion gases therefrom, and heating surfaces extending inside and along said conduit and forming longitudinal interspaces for the passage of the gases, in combination the improvement comprising tornado-flow excitation means joined with said chamber and including at least one of said supply means for producing and maintaining in said firing chamber a tornado-flow of gas-entrained fuel particles to issue a twisting rotational flow of smoke gases from said chamber into and through said interspaces along said heating surfaces, said tornado-flow excitation means comprising peripherally distributed fluid injection nozzles laterally entering into said firing chamber in a tangential and downwardly inclined direction, said fuel supply means comprising an axial inlet tube having an opening at the top and protruding from below into said chamber and forming at the bottom of said chamber an annular, upwardly open space for ash and slag to be drained, said injection nozzles being located at respectively different heights above the opening of said fuel inlet tube for exciting a potential circulating flow component of the tornado-flow.

7. In a steam generator according to claim 6, said fuel inlet tube comprising twist-imparting guide means in said opening for pie-exciting a rotary flow of the fuel entering into said chamber.

8. A steam generator according to claim 6, comprising additional injection means extending tangentially with respect to said chamber and located below said injection nozzles, the injecting direction of said additional injection means extending at an angle to the advancing travel of said circulating flow component so as to cause the formation of suspended ring-shaped accumulations of particles.

9. In a steam generator according to claim 8, said additional injection means comprising gas nozzles extending substantially in planes perpendicular to the axis of said chamber.

10. In a steam generator according to claim 8, said additional injection means comprising gas nozzles and being located at several heights between said downwardly inclined injection nozzles and said fuel inlet opening.

11. In a steam generator according to claim 8, said additional injection means comprising gas; nozzles and being located at several heights between said fuel inlet opening and the bottom of said chamber.

References Cited UNITED STATES PATENTS 1,917,275 7/1933 Rossman et a1. 122-235 2,793,626 5/1957 Hubel 122-235 2,939,434 6/1960 Steinert 122-235 FOREIGN PATENTS 727,218 3/1955 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner, 

